The present invention relates to a multicolor image-forming material for forming a full color image of high definition with a laser beam, and a method for forming a multicolor image. In particular, the present invention relates to a multicolor image-forming material which is useful for forming a color proof (DDCP: direct digital color proof) or a mask image from digital image signals by laser recording in the field of printing, and a method for forming a multicolor image.
In the field of graphic arts, printing of a printing plate is performed with a set of color separation films formed from a color original by a lith film. In general, color proofs are formed from color separation films before actual printing work for checking an error in the color separation step and the necessity for color correction. Color proofs are desired to realize high definition which makes it possible to surely reproduce a half tone image and have performances such as high stability of processing. Further, for obtaining color proofs closely approximating to an actual printed matter, it is preferred to use materials which are used in actual printing as the materials for making color proofs, e.g., the actual printing paper as the base material and pigments as the coloring materials. As the method for forming a color proof, a dry method not using a developing solution is strongly desired.
As the dry method for forming color proofs, a recording system of directly forming color proofs from digital signals has been developed with the spread of electronized system in preprocessing of printing (pre-press field) in recent years. Such electronized system aims at forming in particular high image quality color proofs, generally reproduces a dot image of 150 lines/inch or higher. For recording a proof of high image quality from digital signals, laser beams capable of modulation by digital signals and capable of finely diaphragming recording light are used as recording heads. Therefore, the development of an image-forming material having high recording sensitivity to laser beams and exhibiting high definition property capable of reproducing highly minute dots is required.
As the image-forming material for use in a transfer image-forming method using laser beams, a heat fusion transfer sheet comprising in the order of a support having a light-to-heat converting layer which absorbs laser beams and generates heat, and an image-forming layer which contains a pigment dispersed in components such as a heat fusion type wax and a binder is known (JP-A-5-58045 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)). In the image-forming method using such an image-forming material, an image-forming layer corresponding to the area of a light-to-heat converting layer irradiated with laser beams is fused by heat generated in that area and transferred onto an image-receiving sheet arranged on the transfer sheet by lamination, thus a transferred image is formed on the image-receiving sheet.
Further, a heat transfer sheet comprising a support having provided thereon a light-to-heat converting layer containing a light-to-heat converting material, an extremely thin heat-peeling layer (from 0.03 to 0.3 xcexcm), and an image-forming layer containing a coloring material in this order is disclosed in JP-A-6-219052. In this heat transfer sheet, the bonding strength between the image-forming layer and the light-to-heat converting layer bonded through the intervening heat-peeling layer is reduced by laser beam irradiation, as a result, a highly minute image is formed on an image-receiving sheet arranged on the heat transfer sheet by lamination. The image-forming method by the heat transfer sheet utilizes so-called ablation, specifically the heat-peeling layer partially decomposes at the area irradiated with laser beams and vaporizes, thereby the bonding strength of the image-forming layer and the light-to-heat converting layer at that area is reduced and the image-forming layer at that area is transferred to the image-receiving sheet laminated thereon.
These image-forming methods have various advantages that an actual printing paper provided with an image-receiving layer (an adhesion layer) can be used as the material of an image-receiving sheet, and a multicolor image can be easily obtained by transferring images different in colors in sequence on the image-receiving sheet. In particular, the image-forming method utilizing ablation has the advantage that highly minute image can be easily obtained, and so these methods are useful for forming a color proof (DDCP: direct digital color proof) or a highly minute mask image.
DTP is prevailing more and more and the intermediate process using films is omitted when CTP (computer to plate) is used, and the need for proof is shifting from analog proof to DDCP. In recent years the demand for large sized high grade DDCP highly stable and excellent in coincidence in printing has increased.
High definition printing can be effected according to a heat transfer method by laser irradiation, and as the laser heat transfer methods, (1) a laser sublimation method, (2) a laser ablation method, and (3) a laser fusion method are conventionally used, but any of these methods has a drawback such that the shape of a recorded dots are not sharp. In (1) a laser sublimation method, since dyes are used as the coloring material, the approximation of proofs to printed matters is not sufficient, further, since this is a method of sublimating coloring materials, the outline of a dot is fuzzy, and so definition is not sufficiently high. On the other hand, since pigments are used as the coloring materials in (2) a laser ablation method, the approximation to printed matters is good, but since this is a method of sputtering coloring materials, the outline of a dot is also fuzzy as in the sublimation method, and so definition is not sufficiently high. Further, in (3) a laser fusion method, a molten substance flows, and so the outline of a dot is not also clear.
Moreover, these image-forming materials comprising a heat transfer sheet and an image-receiving sheet contain a matting agent in the constituting layers to improve the quality of the image to be obtained, but there is such a problem that the contact of the heat transfer sheet and the image-receiving sheet becomes insufficient partially at recording time due to the cohesion of the matting agent, which hinders transferring and causes so-called spot-like image blank areas (i.e., clear spots). Further, the pot life of a coating solution containing a matting agent is relatively short and inconvenient.
Accordingly, the object of the present invention is to solve the above-described problems of the prior art technique and to accomplish the following objects. That is, an object of the present invention is to provide a large sized high grade DDCP which has high quality and is highly stable and excellent in coincidence in printing. Specifically, the present invention is characterized in that: 1) a heat transfer sheet can provide excellent sharpness of dots and stability by transfer of a membrane of coloring material, which is not influenced by light sources of illumination as compared with the pigment material and the printed matter, 2) an image-receiving sheet can receive stably and surely the image-forming layer in a heat transfer sheet by laser energy, 3) transfer to actual printing paper can be effected corresponding to the range of at least from 64 to 157 g/m2 such as art paper (coat paper), mat paper and finely coated paper, delicate texture can be imaged, and a high-key part can be reproduced accurately, and 4) extremely stable transfer pealing property can be obtained.
A further object of the present invention is to provide a method for forming a multicolor image which can form an image having good image quality and stable transfer image density on an image-receiving sheet even when recording is performed by multi-beam laser beams of high energy under different temperature and humidity conditions.
Still further object of the present invention is to provide an image-forming material capable of using a coating solution having a long pot life and not accompanied by the blank area (i.e., the clear spot) of an image resulting from a matting agent, and a producing method of such a material.
That is, the present invention has been attained by the following means.
(1) A multicolor image-forming material which comprises an image-receiving sheet comprising a support having thereon a coating layer including at least an image-receiving layer, and a plurality of heat transfer sheets each comprising a support having coating layers including at least a light-to-heat converting layer and an image-forming layer, wherein the ratio of the optical density (OD) of the image-forming layer in each heat transfer sheet to the layer thickness, OD/layer thickness (xcexcm unit), is 1.50 or more, the recording area of a multicolor image of the heat transfer sheet is a size of 515 mm or more multiplying 728 mm or more, the definition of a transferred image is 2,400 dpi or more, and the coating layer in the image-receiving sheet and/or the coating layers in each heat transfer sheet has at least one layer containing a dispersant and a matting agent having an average particle size of from 0.05 to 50 xcexcm.
(2) The multicolor image-forming material as described in the above item (1), wherein the dispersant is a surfactant and/or a polymer.
(3) The multicolor image-forming material as described in the above item (1) or (2), wherein the average particle size of the matting agent is from 0.1 to 30 xcexcm.
(4) A method for manufacturing the multicolor image-forming material as described in the above item (1), (2) or (3) which comprises the steps of dispersing the matting agent in a dispersion medium with the dispersant in advance to prepare a coating solution containing the dispersed matting agent, coating and drying the prepared coating solution to form the layer containing the matting agent, to thereby obtain the multicolor image-forming material.
(5) The method for manufacturing the multicolor image-forming material as described in the above item (4), wherein the water content in the dispersion medium at dispersing the matting agent is 50% or less.
(6) The multicolor image-forming material as described in the above item (1), wherein any coating layer in the heat transfer sheet and/or the image-receiving sheet contains spherical fine particles having an average particle size of from 0.10 to 3.0 xcexcm and a particle size distribution (L25/L75) of 2.0 or less.
(7) The multicolor image-forming material as described in the above item (6), wherein the spherical fine particles are amorphous fine particles.
(8) The multicolor image-forming material as described in the above item (6) or (7), wherein the spherical fine particles have an average particle size of from 1.1 to 3.0 xcexcm.
(9) The multicolor image-forming material as described in the above item (6), (7) or (8), wherein the spherical fine particles have a specific gravity of from 1.1 to 3.5 at 25xc2x0 C.
(10) The multicolor image-forming material as described in the above item (6), (7), (8) or (9), wherein the spherical fine particles have a specific gravity of from 1.1 to 1.4 at 25xc2x0 C.
(11) The multicolor image-forming material as described in the above item (1) or (16), wherein any coating layer in either the heat transfer sheet or the image-receiving sheet contains an acryl-based polymer having a glass transition point of from 10 to 120xc2x0 C.
(12) The multicolor image-forming material as described in the above item (11), wherein the light-to-heat converting layer in the heat transfer sheet contains an acryl-based polymer having a glass transition point of from 10 to 120xc2x0 C.
(13) The multicolor image-forming material as described in the above item (11) or (12), wherein the acid value of the acryl-based polymer is 300 or less.
(14) The multicolor image-forming material as described in the above item (11), (12) or (13), wherein the acryl-based polymer has structure containing a styrene derivative moiety in the polymer molecule.
(15) The multicolor image-forming material as described in any of the above items (1) to (14), wherein the definition of a transferred image is 2,600 dpi or more.
(16) The multicolor image-forming material as described in any of the above items (1) to (15), wherein the ratio of the optical density (OD) of the image-forming layer in each heat transfer sheet to the layer thickness, OD/layer thickness (xcexcm unit), is 1.80 or more.
(17) The multicolor image-forming material as described in any of the above items (1) to (16), wherein the recording area of a multicolor image is 594 mm multiplying 841 mm or more.
(18) The multicolor image-forming material as described in any of the above items (1) to (17), wherein the contact angle of the image-forming layer in each heat transfer sheet and the image-receiving layer in the image-receiving sheet with water is from 7.0 to 120.0xc2x0.
(19) The multicolor image-forming material as described in any of the above items (1) to (18), wherein the ratio of the optical density (OD) of the image-forming layer in each heat transfer sheet to the layer thickness, OD/layer thickness (xcexcm unit), is 1.80 or more, and the contact angle of the image-receiving sheet with water is 89xc2x0 or less.
(20) The multicolor image-forming material as described in any of the above items (1) to (18), wherein the ratio of the optical density (OD) of the image-forming layer in each heat transfer sheet to the layer thickness, OD/layer thickness (xcexcm unit), is 2.50 or more.
(21) A method for forming a multicolor image using the image-receiving sheet as described in any of the above items (1) to (20) and four or more heat transfer sheets as described in any of the above items (1) to (20) comprising the steps of superposing the image-forming layer in each heat transfer sheet and the image-receiving layer in the image-receiving sheet vis-a-vis, and irradiating the heat transfer sheet from the support side with laser beams and transferring the area of the image-forming layer subjected to laser beam irradiation onto the image-receiving layer in the image-receiving sheet, to thereby effect image-recording, wherein the image-forming layer in the laser beam irradiation area is transferred to the image-receiving sheet in a membrane state.